1. Field of the Invention
The present invention relates to a combustor, particularly to a gas turbine combustor in which additional air can be supplied by a bypass passage.
2. Description of the Related Art
In general, a gas turbine combustor is disposed between a compressor and a turbine. Fuel F is supplied to a gas turbine combustor through a fuel supplying passage of a nozzle portion in the gas turbine combustor. Compressed air A compressed by the compressor is supplied to a casing of the gas turbine combustor and, then enters the nozzle portion through an inlet portion of the nozzle portion and is supplied to the combustor through a swirler. Thus, the compressed air A and the fuel F are mixed and burned in the combustor. High temperature gas produced by combustion of the compressed air A and the fuel F is discharged from the combustor through a tail portion thereof to drive the turbine provided on the downstream side of the gas turbine combustor in the direction of air flow.
A bypass passage having a bypass valve is provided on one side of the combustor tail portion. When the output of the turbine varies, the bypass valve is opened and closed so that the compressed air A in the casing is supplied to the combustor tail portion through the bypass passage from the inlet portion to an outlet portion thereof. Accordingly, additional compressed air A is supplied to the combustor tail portion so that the air-fuel ratio, i.e., the ratio of air to fuel in the gas turbine combustor can be maintained at an appropriate value.
However, the bypass passage is attached to only one side of the combustor in a known gas turbine combustor. Therefore, when additional compressed air A is supplied to the combustor tail portion through the bypass passage, the concentration of fuel in the combustor tail portion is locally decreased in the vicinity of the outlet of the bypass passage.
In general, when the ratio of combustion air to fuel is high, the flame becomes unstable due to lack of fuel. In addition, when the ratio of fuel to combustion air is high, NOx tends to easily occur. In other words, the flame tends to become unstable in the vicinity of the outlet of the bypass passage, and NOx tends to occur at the opposite side of the outlet, in a cross section of the combustor tail portion. Therefore, if the bypass valve is adjusted to maintain the air-fuel ratio at a substantially constant value, it is necessary for the additional compressed air passing through the bypass passage to be uniformly supplied to the combustor tail portion in the circumferential direction thereof.
The additional compressed air A is supplied to the combustor, particularly to the combustor tail portion via the outlet of the bypass passage, so that the temperature in the vicinity of the outlet is locally decreased, and unevenness of the temperature distribution occurs in a cross section of the combustor tail portion.
Accordingly, the object of the present invention is to provide a combustor in which the compressed air passing through the bypass passage is uniformly supplied into the combustor tail portion in the circumferential direction thereof, and unevenness of the temperature distribution in a cross section of the combustor tail portion is reduced.